Brewed a batch yesterday that had a preboil volume of 7.5 gallons and 1.050 gravity reading with temperature accounted for. After the boil and adding a whirlfloc tablet I ended up with ~4.5 gallons at 1.048. Now this seems physically impossible that at a lower volume of water my SG would drop. The only thing I can think of is I used pilsner malt which I've heard has higher protein that precipitated out and has a an effect on gravity? Anyone else have similar experience with SG dropping after boiling/cooling where hot and cold break sediment/proteins are removed? Or is my hydrometer going bad?
Before and after WhirLpoOL HydroMeTer Readings
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Nothing to do with the grains or whirlpool or hops and everything to do with measurement error in one or more of the following
preboil volume
preboil gravity
post boil volume
post boil gravity
Taking gravities at very high temperatures will commonly result in error even if using corrective algorithms. There is too much room for error. Cool the samples to the correct temp for the hydrometer you use. (It's written on the guage)
preboil volume
preboil gravity
post boil volume
post boil gravity
Taking gravities at very high temperatures will commonly result in error even if using corrective algorithms. There is too much room for error. Cool the samples to the correct temp for the hydrometer you use. (It's written on the guage)
d3track
Are you sure about that?
Recipe? Something is being measured and or read incorrect
cantrell00
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Make certain your preboil volume is thoroughly mixed. Stratification of varying gravity are a common problem with preboil hydrometer samples.
You collected that second sample from near surface and the wort stratified. You need to collect the hydrometer or refractometer sample from wort that is freshly mixed or it will separate into a lower gravity layer near the wort surface.
This says you have lost approximately
7.5*8.34*1.050*plato(1.050)/100 - 4.5*8.34*1.048*plato(1.048)/100 = 3.45072
pounds of extract (almost half of it). That is rather more than one would reasonably expect to be lost as break material. Thus clearly either your measurements are wrong or you lost the three gallons as boil over rather than evaporation.
That's possible too. Check it. In water it should, obviously, read close to 1.000. Put a beaker or glass or pot or whatever you have on a decent scale and tare it. Add 1 unit of sucrose (100 grams, 1 Oz....) and then add water until the scale reads 10 units (1000 grams, 10 Oz). Stir to dissolve the sugar. The result is a 10 °P solution with SG = 1.04003 (20 °C hydrometer).
+1 on the runnings simply not being mixed enough.
If you feel like seeing for yourself, take your preboil wort without mixing, check the gravity 3 ways, one sample only from the top, one only from the bottom, and then a third with it all mixed. Low, high, and accurate.
Also agree on chilling the sample down appropriately. Chilling for a hydrometer isn't ideal in my book, which is why for all hot-side readings I use a refractometer. Rather than waiting even on the freezer to chill several ounces, you can chill the few drops for a refractometer in seconds.
If you feel like seeing for yourself, take your preboil wort without mixing, check the gravity 3 ways, one sample only from the top, one only from the bottom, and then a third with it all mixed. Low, high, and accurate.
Also agree on chilling the sample down appropriately. Chilling for a hydrometer isn't ideal in my book, which is why for all hot-side readings I use a refractometer. Rather than waiting even on the freezer to chill several ounces, you can chill the few drops for a refractometer in seconds.
Wort, or any similar solution, does not stratify. Quite the opposite. If it is stratefied it de-stratifies. To see this do the following simple experiment. Draw a glass of tap water. Carefully add some honey (simulated wort of SG ~ 1.32) preferably from a squirt bottle type dispenser so that a thin stream of honey falls through the water to pool on the bottom of the glass. Add enough so that there is a clearly discernible layer on the bottom. Set the glass in a warm place (same thing happens in a cool place but in a warm place it's faster) and leave it undisturbed.
In the honey layer the chemical potential of fructose and glucose is very high compared to that in the water layer and, as there is nothing to prevent the movement of these molecules, they will flow from high to low potential. They are said to 'diffuse' into the water as a result of the kinetic energy they posses which manifests itself in molecular translational motion. The same argument applies to water molecules except in the opposite direction. Water molecules flow into the honey layer where their chemical potential is lower. After even a few hours the boundary between the layers is blurred. Eventually, the glass will contain a glucose/fructose solution of uniform composition.
Now out of the lauter tun from which the first runings are denser than the last, you may well have stratification as diffusion is a slow process. But once the heat is turned on and certainly once ebullition is achieved, the wort will be pretty thoroughly mixed. OP spoke of boiled wort which had, in addition to the mixing of boiling, been further mixed by whirlpooling. I doubt his problem is stratification.
Consider (and do, if you like) the related experiment in which you dissolve a tsp of honey in a cup of hot water, this time stirring to be sure it is all 'dissolved'. Now set that container aside and wait for the stratification to occur. To those who have studied such things note that after thorough mixing any sugar molecule can be anywhere in the glass. Were stratification to take place a sugar molecule would be more likely to be in a denser layer. The number of states accessible to it would, thus, be reduced (fewer locations it can be in) without having done any work on the system and this is a clear violation of the second law. Second law violations do occur on certain sites here on the web where you can buy plans for motors that produce more power than you supply but in the real world the second law is inviolate.
He didn't mention any mixing for his preboil reading though- I think people were assuming that it wasn't the post-whirlpool reading that was inaccurate, but rather the preboil reading, which hadn't been sitting long enough to become consistent between first and last runnings.
While I was really more concerned with clarifying the misconception that wort will stratify, your point is taken. Looking into things a little further, however, if we assume the post whirlpool reading is correct he has
4.5*8.34*1.048*plato(1.048)/100 = 4.68522
lbs of extract. In 7.5 gal of wort that same extract would give us an average wort density of 7.13 °P corresponding to SG = 1.0283. OP measured 1.050. The bad mixing thesis says that he took a sample from the top of the kettle where the wort density would be less than the average. Thus the poor mixing theory doesn't seem to stand up from this POV either. IF, OTOH, he sampled the first runnings he might have gotten 1.05.
I'm not saying that post collection/pre boil wort doesn't stratify to some extent (at least initially) nor that one shouldn't stir such wort thoroughly in order to get a valid reading but rather that non uniform wort doesn't seem to be the explanation here.
4.5*8.34*1.048*plato(1.048)/100 = 4.68522
lbs of extract. In 7.5 gal of wort that same extract would give us an average wort density of 7.13 °P corresponding to SG = 1.0283. OP measured 1.050. The bad mixing thesis says that he took a sample from the top of the kettle where the wort density would be less than the average. Thus the poor mixing theory doesn't seem to stand up from this POV either. IF, OTOH, he sampled the first runnings he might have gotten 1.05.
I'm not saying that post collection/pre boil wort doesn't stratify to some extent (at least initially) nor that one shouldn't stir such wort thoroughly in order to get a valid reading but rather that non uniform wort doesn't seem to be the explanation here.
Unfortunately, there is a preconception that wort is purely a solution. Wort is also a suspension and the stratification that is known to thousands of brewers is not an anomoly. It is an expectation and a good brewer is going to plan and correct for that real "problem".
The bright wort that enters my kettle is a solution of sugars, proteins, salts and lots of other things (if I do a good job lautetring).
No, it isn't unless one has allowed fines to survive sparging. If, of course, one boils wort in the right pH range dissolved protein molecules will aggregate until they are too big to stay in solution whence they precipitate and go into suspension. Also, protein molecules are more soluble in hot wort than cold. We have all seen our bright wort become turbid when we cool it for a hydrometer reading. This is from suspended protein.
Perhaps there is confusion as to what a suspension is. Things in suspension are not dissolved but are solid particles that are (by definition) large enough (> 1 µ) that if allowed will, on their own, settle or float. The interesting thing about such particles is that they have no effect on SG. If they are denser than water they just fall to the bottom. One must be careful that they do not fall on the shoulders of a hydrometer though! Here's an opportunity to upset your SG reading if your bright wort turns cloudy when you cool it. If, however, the suspended protein does not settle to the bottom of the jar that is an indication that its density is close to that of water and the error introduced will be small. Spin your hydrometer to throw any protein off the shoulders and be on the safe side. If suspended matter is lighter than water, floats and also has no effect on hydrometer reading (we assume it doesn't stick to the bottom). Put a hydrometer into a swimming pool. Now have a SCUBA diver jump in. The hydrometer reading doesn't change no matter how he adjusts his BC (unless he is standing on the shoulder of the hydrometer).
Stratification can occur under some circumstances but it is completely explained if we realize that bright wort is indeed a solution with nothing suspended in it. As noted above anything suspended will either float or sink to the bottom (as do the small quantity of fines that always seem to make it into my kettle no matter how carefully I vorlauf). The experiment with the honey makes the mechanism clear. The first runnings are dense. They tend to go to or stay near the bottom as lighter wort is pumped in. If you fill your kettle from the bottom then the lighter stuff has to make its way through the dense layer to reach the top and this, of course, results in some mixing. But were I to fill from above and keep the fill tube just below the surface as the later runnings came in I would be able to create, with some care, the layering we see in the honey experiment.
Now the smart brewer is going to start the heat before the kettle is full. The heating element is close to the bottom of the kettle and so vertical convection currents are set up and these mix the wort. In such a setup no stirring is necessary though I never take a measurement until the boil has been reached thus insuring that sufficient mixing has taken place. People who proceed differently, for example anyone who does not apply the heat before the sparge is finished could have stratification and would be advised to stir before taking a reading. As I determine OG by back calculation from ABV these readings aren't that important to me anyway but they always compare pretty closely to the back calculated values.
So it isn't necessarily an expectation at all. The good brewer will want to understand the physics as it applies to his equipment and practices and act accordingly. If you don't understand the physics or don't want to, just stir. It's easy enough!
cantrell00
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Here is a riddle. Which one of you two can piss higher up a rope?
Jesus H!
Jesus H!
If you don't want to read a discussion/thread there is an unsubscribe button.
I don't know about you but I learn a great deal from these two guys.
i think I bit of respect is warranted, or a the very least a modicum of common manners wouldn't be out of order.
No one here on HBT is a shrinking violet in need of defending. Still, sometimes things need to be said.
Seriously, unsubscribe. It's in the thread tools tab. You can sleep easy knowing you won't be subjected to the possibility of learning something new.
Apparently you need to be reminded that this is the place for
"In depth technical threads related to the biology and chemistry of home brewing." If this is beyond your intellectual capacity stick with the other topics.
In this case a statement, unsupportable by brewing (or other) science was made and the reasons why it is so were set out in some detail. This was followed by another unsupportable statement and that was also corrected. Precisely, if you can, which part of this comprises a pissing contest?
I had a post flagged for deletion as off-topic, something about a rope. But since there are replies, it makes it hard to delete.
So let me just suggest to any others who chose to comment to please keep on topic or refrain from posting. Or, like your momma told you, "If you can't say something nice (on topic, at least), then don't say anything at all".
If people want to ask the opinions of others in the Brew Science forum, a modicum of respect for the discussion is warranted.
People do NOT have to agree- that is not realistic. But keeping on topic, and refraining from personal comments IS realistic.
Ok, so to go back to on topic-
One thing that struck me is something very simple. The OP could have simply taken a reading of the preboil wort at a mash out/sparge temperature and used a temperature correction table (with a hydrometer).
Since anything over about 100 degrees delivers a notoriously inaccurate reading, it could be something that simple.
Any more science-y than that is way over my head, but I thought I'd through that out there, as it happened to me many times.
So let me just suggest to any others who chose to comment to please keep on topic or refrain from posting. Or, like your momma told you, "If you can't say something nice (on topic, at least), then don't say anything at all".
If people want to ask the opinions of others in the Brew Science forum, a modicum of respect for the discussion is warranted.
People do NOT have to agree- that is not realistic. But keeping on topic, and refraining from personal comments IS realistic.
Ok, so to go back to on topic-
One thing that struck me is something very simple. The OP could have simply taken a reading of the preboil wort at a mash out/sparge temperature and used a temperature correction table (with a hydrometer).
Since anything over about 100 degrees delivers a notoriously inaccurate reading, it could be something that simple.
Any more science-y than that is way over my head, but I thought I'd through that out there, as it happened to me many times.
Natdavis777
Well-Known Member
Ive been meaning to do an experiment where I take a sample of unstirred wort from the top, the bottom, and then the same from freshly stirred wort. I have experienced this phenomenon in the past, where my post boil gravity seemed to go backwards. A caveat, I only experienced this a few times when I first started brewing, and I was batch sparging. I cannot exactly recall when I took the samples. My process/equipment has vastly changed since then, so I cant rule out a procedural error, as I have not experienced it since then.
Currently I take pre boil samples right as the wort boils (ensuring for peace of mind that the wort is thoroughly mixed) and the post boil right before flame out (same reasoning).
Currently I take pre boil samples right as the wort boils (ensuring for peace of mind that the wort is thoroughly mixed) and the post boil right before flame out (same reasoning).
Glad you didn't. If someone wants to advertise his lack of intellect in a public forum I think he should be allowed to do so but I confess that I do not understand why so many seem to be so willing to do just that.
I feel compelled to answer the question but must first, of course, ask the qualifying question "Hands or no hands?". In either case, given my advanced years, I'm sure the day would go to Martin.
For someone who builds their own water profiles Martin and AJ are extremely valuable to me. Even if they debate a little it is always a good read and I learn something new each time. Don't kick a gift horse in the mouth.
Just an update on the diffusion experiment described in #8: It's been a week since I posted that and I set up the experiment described when I did. While diffusion is definitely taking place it is slow. The intensely colored honey layer that was initially perhaps 1/4" thick has disappeared to be replaced with a less intensely colored layer but that is, at this point, only about 1 - 1/4" thick. None of the water is entirely clear.
I'm glad to see an interesting debate on the nature of wort stratification, and can't help but give my two cents as a professional brewer. First, a small primer on the system and process scale I'm used to:
On the system I use at work we have a 20 bbl capacity kettle with floor and lower side jacket steam heating. Kettle fill occurs at, roughly, 5.4 gpm, through a tangential port roughly 1 foot off the bottom of the kettle for a final pre-boil fill of 650 gallons. The jackets are turned on once ~30 gallons are in the kettle (just enough to cover the floor), and boil ramp-up takes the entire fill duration of ~2 hours.
Once the kettle is full we need to wait until we have a rolling boil, as defined by 6-9" border of hard boiling liquid along the edge, before we take our pre-boil gravity via dip bucket along the outer edge of the kettle.
Once our 60 minutes boil is done we're down to ~630 gallons, and before we shut the steam jackets and kettle stack vent off we need to take another gravity reading, again from the outer edge. It's vital that a full pull along the outer edge, from top to bottom, is done at this point to ensure an accurate reading.
And, ideally, that'd be it. During the boil stratification isn't an issue, but the moment heat is removed from the system that very same stratification that ajdelange says shouldn't happen? Yeah, it happens. If I forget to take my post boil gravity while still boiling my kettle draw will be inaccurate, and my final gravity measure can be off by as much as 0.2-0.4*Plato. The only solution? Take a hydrometer reading off of the chiller once the kettle volume is ~615-520 gallons, or just take a hydrometer reading off of the filled fermenter once the kettle is empty.
I'm a microbiologist, not a chemist, so I can't say exactly why stratification occurs. All I know is that it does, on a professional volume using wort as the extract source, and I see no reason why the same physics and chemistry would not also occur at smaller scales.
On the system I use at work we have a 20 bbl capacity kettle with floor and lower side jacket steam heating. Kettle fill occurs at, roughly, 5.4 gpm, through a tangential port roughly 1 foot off the bottom of the kettle for a final pre-boil fill of 650 gallons. The jackets are turned on once ~30 gallons are in the kettle (just enough to cover the floor), and boil ramp-up takes the entire fill duration of ~2 hours.
Once the kettle is full we need to wait until we have a rolling boil, as defined by 6-9" border of hard boiling liquid along the edge, before we take our pre-boil gravity via dip bucket along the outer edge of the kettle.
Once our 60 minutes boil is done we're down to ~630 gallons, and before we shut the steam jackets and kettle stack vent off we need to take another gravity reading, again from the outer edge. It's vital that a full pull along the outer edge, from top to bottom, is done at this point to ensure an accurate reading.
And, ideally, that'd be it. During the boil stratification isn't an issue, but the moment heat is removed from the system that very same stratification that ajdelange says shouldn't happen? Yeah, it happens. If I forget to take my post boil gravity while still boiling my kettle draw will be inaccurate, and my final gravity measure can be off by as much as 0.2-0.4*Plato. The only solution? Take a hydrometer reading off of the chiller once the kettle volume is ~615-520 gallons, or just take a hydrometer reading off of the filled fermenter once the kettle is empty.
I'm a microbiologist, not a chemist, so I can't say exactly why stratification occurs. All I know is that it does, on a professional volume using wort as the extract source, and I see no reason why the same physics and chemistry would not also occur at smaller scales.
Forgive me but I trust the laws of physics more than your observations. It is not at all clear what you are doing but it seems that you are claiming stratification based on some noise in your readings. If you are lowering a container to the bottom of the kettle whose mouth can be closed while it is at depth and doing the same at mid level and surface and find different gravities in those samples when all cooled to the same temperature then you have stratification but I rather doubt that would be the case. I will offer a possible explanation as to why you might get stratification after shutting off the steam below.
But let's try common sense here. Do other sugar solutions you have familiarity with such as honey, Lyles syrup, corn syrup, maple syrup... stratify? No. If they did you would be instructed to 'shake before using'. Thus you are claiming that a syrup of maltose (mostly) dissolved in water behaves differently from these other sugar solutions. What's different here?
I suggested above that there might be an explanation for temporary layering and that is that when the steam is shut off the jackets stay hot for a while whereas the surface wort cools. Thus the surface wort will, initially, be denser than the wort at the bottom of the kettle but the composition (grams of sugar per 100 g of solution) will be the same and when you bring the samples to the same temperature you should get the same °P readings.
Aside: The diffusion (the reason layering does not take place absent temperature gradients) experiment is about 2 weeks running now and while the bottom layer is definitely diffused and all the water is colored the color is still more intense closer to the bottom. Diffusion of an 85 °P sugar (honey) solution into water is slow at room temperature,
But let's try common sense here. Do other sugar solutions you have familiarity with such as honey, Lyles syrup, corn syrup, maple syrup... stratify? No. If they did you would be instructed to 'shake before using'. Thus you are claiming that a syrup of maltose (mostly) dissolved in water behaves differently from these other sugar solutions. What's different here?
I suggested above that there might be an explanation for temporary layering and that is that when the steam is shut off the jackets stay hot for a while whereas the surface wort cools. Thus the surface wort will, initially, be denser than the wort at the bottom of the kettle but the composition (grams of sugar per 100 g of solution) will be the same and when you bring the samples to the same temperature you should get the same °P readings.
Aside: The diffusion (the reason layering does not take place absent temperature gradients) experiment is about 2 weeks running now and while the bottom layer is definitely diffused and all the water is colored the color is still more intense closer to the bottom. Diffusion of an 85 °P sugar (honey) solution into water is slow at room temperature,
Argue all you like but, on our commercial scale setting, with standard gravity wort, boil, and hopping, we observe post-boil kettle gravity stratification.
We use commercial grade hydrometers with temperature calibration, pre-test wort chillers with temperature confirmation, and bi-weekly accuracy testing testing of our equipment. We also have a standard commercial height vs diameter kettle ratio,follow standardized testing protocols, and observe stratification in our wort density so regularly countering it is part of our testing protocol.
Wort is not composed of strictly maltose, nor is it an even density when introduced into the tank. You're arguing against a phenomenon that is both well know, and I would have to conclude that you're arguing without a complete grasp of the chemistry or physics involved.
You're also doing a diffusion experiment, which is awesome. But, unfortunately, you're running a limited comparison small scale test using similar, but not identical, ingredients, dimensions, temperature, process, or time. Every difference between your experiment and an actual brew kettle wort boil reduces the relevance of the experiment to the brewing environment.
When your hypothesis doesn't match the full scale data, don't blame the data.
We use commercial grade hydrometers with temperature calibration, pre-test wort chillers with temperature confirmation, and bi-weekly accuracy testing testing of our equipment. We also have a standard commercial height vs diameter kettle ratio,follow standardized testing protocols, and observe stratification in our wort density so regularly countering it is part of our testing protocol.
Wort is not composed of strictly maltose, nor is it an even density when introduced into the tank. You're arguing against a phenomenon that is both well know, and I would have to conclude that you're arguing without a complete grasp of the chemistry or physics involved.
You're also doing a diffusion experiment, which is awesome. But, unfortunately, you're running a limited comparison small scale test using similar, but not identical, ingredients, dimensions, temperature, process, or time. Every difference between your experiment and an actual brew kettle wort boil reduces the relevance of the experiment to the brewing environment.
When your hypothesis doesn't match the full scale data, don't blame the data.
You are making observations which cause you to conclude that stratification is taking place. If your observations are flawed the conclusion is invalid.
For this kind of work you should be using a digital densitometer. I understand, hwever, that those things are too expensive for any but pretty good sized breweries.
The ASBC MOA calls for the use of a densitometer.
The problem I have in coming up with an explanation is that you are rather mysterious about what measurements you are actually taking, where and how.
No it isn't but that's irrelevant. Glucose and maltotriose, to pick a couple of other sugars are also uncharged, non polar molecules and thus not subject to any mechanism that would cause migration in a uniform solution. The ions of the salts are charged and thus subject to ionic strength effects but still flow along line of chemical potential gradient
Which tank are you talking about? You are going to have to be more precise in your explanations if you expect me to help you understand why you are seeing what you are seeing. But even if you are I cannot promise to be able to do that. Would you not agree that it is well mixed during the boil?
It is well known that there are lots of ways to get stratification in the short term. Thoroughly mixing a solution and letting it stand isn't one of them unless a temperature gradient is applied. Stratification of a solution at uniform temperature would violate the second law of thermodynamics as I explained in an earlier post.
Well you'd be right of course as I don't have a complete grasp of anything but I would have to observe that your arguments show a lack of undetrstanding of basic p-chem. Didn't you have to take a course in that on you path to your microbiology degree?
Irrelevant. Can you describe any solution in which there is a concentration gradient and in which diffusion does not occur. Again I am surprised at the lack of knowledge here as diffusion in biological systems is very important in my limited understanding of such things.
No it doesn't as explained above. I didn't have to do the diffusion experiment to convince myself. I knew exactly what would happen (except that I thought it would happen faster). The diffusion experiment was suggested as a simple experiment that people with limited experience in such things could do to convince themselves that stratification cannot take place under equilibrium conditions. Now I grant you that you are not seeing equilibrium in many places in the brewing process. But a wort thoroughly mixed my a vigorous boil would be a place where one would expect equilibrium to have been reached. At the conclusion of the boil, you maintain, something happens to upset the equilibrium but have no idea as to what that might be. Perhaps it is the temperature gradient I proposed in my earlier post but as I said then I don't think even that would result in temperature adjusted samples being different.
Quite the opposite. When the data doesn't match the hypothesis, the first thing one does is question the data. Especially when the hypothesis is as here the null hypothesis (basic physical laws say that stratification shouldn't occur) the very first thing you do is question the data and that is what I am doing here. The mature approach is to say 'The data don't match what the physics predict. Why is that?' and then dive in and find out why. Sometimes it's instrument error, sometimes it's software error, sometimes it's operator error and sometimes it's none of those but something you were unaware of or didn't think of or something you don't know about. The last is what you are suggesting here and I readily allow that this is possible. You can be sure I'll be experimenting with this next time I brew.
Questioning the data that does not match a hypothesis lies at the very core of scientific discovery.
Two examples on scale of the incredibly tiny and incredibly huge.
- The Lamb Shift and the development of quantum electrodynamics
- The seemingly nonsense predictions of special relativity including gravitational lensing and perturbations in the orbit of Mercury. The former being observed many decades after the hypothesis was spawned and the latter being explained by the new hypothesis laying waste to countess wasted hours searching for a hidden planet.
I'm not a pro brewer nor a physicist but have been fortunate to have had the opportunity to study thermodynamics on a fairly rudimentary level. It is clear that stratification in a sugar solution will reduce the entropy of the system.
The scientific model, data should always be questioned first.
You'll get no disagreement with me questioning the data over the hypothesis, but this isn't a one-off data point. This isn't even a couple of times data point that can be explained away as process error or sampling noise. This is a consistent, measurable, observation that shows up in every boil. The simple fact is that our wort gravity displays a stratified density gradient with densest wort at the bottom and lightest wort at the top.
I know what a basic thermodynamics model would say about a stratified solution being more ordered, and thus not the preferred state, but something is causing stratification in our kettles. I'll also admit, since we have a QC workaround that works well enough to ensure batch consistency, that I've never looked deeper into the issue than to note that it occurs and how to still get accurate post-boil OG numbers. This is commercial level beer being produced, and the government tends to get annoyed if our ABV labeling is wrong, so we don't really have the option of bad sampling methods. Getting our numbers wrong can get us shut down.
Since ajdelange has already felt a need to insult my p-chem education and imply I don't know basic thermodynamics I'll look through the literature and see what I can't find before replying again.
I don't think you'll find the answer in thermo because thermo deals with systems at equilibrium and in such systems stratification can't happen. We are looking for some non-equilibrium state phenomena which causes a well mixed system to separate.
I've put a couple of feelers out, so I'm hopeful that some of the guys I know with larger systems and better equipped QC labs might have an answer. I'll let you all know if I find anything out.
Could BugHunter be seeing an issue of temperature stratification, where there is a hot spot at the top of his kettle caused by a vapor cushion or the like? If he does not have the assumed equilibrium of temperature throughout his kettle, would that be why his measurements do not match the expectations?
MandingaBIAB
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I haven't observed stratification with my BIAB system.... It seems that gravity, viability and viscosity are constant in all depths of the kettle, high and low. But, with that being said, I try to give the wort a gentle stir to keep the heavier sugars from accumulating near the bottom of the kettle so it could be a function of stirring that keeps my wort the same.
Yes, I suggested that with a possible mechanism in #22 but wasn't too enamored of that explanation as even though the wort would be denser at the top the mole fractions of the constituents would be the same throughout. Perhaps there is some subtlety I'm missing in that reasoning.
jmpreiks
Well-Known Member
Did you mean denser at the bottom?
No, under this hypothesis, which is, remember, only a hypothesis, the wort at the top is cooler and thus more dense. Now the denser wort isn't going to stay there very long and will, in pretty short order, sink to the bottom and in so doing mix with the lighter stuff there. At the same time the lighter stuff in contact with the jackets will rise so, until the jackets cool to the same temperature as the wort, the convection currents will still flow, lighter wort ascending the sides and denser wort sinking in the center. Mixing will continue though at a slower rate than during the boil.
GotPushrods
Well-Known Member
Forgive me as I haven't read the entire thread, but it seems like there might be 2 phenomenon being discussed here.
There is stratification, then there is just incomplete mixing. I and many others have seen 'strata' when one density wort is transferred onto/under another. However I have never witnessed homogeneous wort which is thoroughly mixed become stratified once again.
Was the OP just about 2 worts that may have never been properly mixed in the first place?
There is stratification, then there is just incomplete mixing. I and many others have seen 'strata' when one density wort is transferred onto/under another. However I have never witnessed homogeneous wort which is thoroughly mixed become stratified once again.
Was the OP just about 2 worts that may have never been properly mixed in the first place?
